title: piRNAs and epigenetic conversion in Drosophila.
abstract: Transposable element (TE) activity is repressed in the Drosophila germline by Piwi-Interacting RNAs (piRNAs), a class of small non-coding RNAs. These piRNAs are produced by discrete genomic loci containing TE fragments. In a recent publication, we tested for the existence of a strict epigenetic induction of piRNA production capacity by a locus in the D. melanogaster genome. We used 2 lines carrying a transgenic 7-copy tandem cluster (P-lacZ-white) at the same genomic site. This cluster generates in both lines a local heterochromatic sector. One line (T-1) produces high levels of ovarian piRNAs homologous to the P-lacZ-white transgenes and shows a strong capacity to repress homologous sequences in trans, whereas the other line (BX2) is devoid of both of these capacities. The properties of these 2 lines are perfectly stable over generations. We have shown that the maternal transmission of a cytoplasm carrying piRNAs from the first line can confer to the inert transgenic locus of the second, a totally de novo capacity to produce high levels of piRNAs as well as the ability to induce homology-dependent silencing in trans. These new properties are stably inherited over generations (n>50). Furthermore, the converted locus has itself become able to convert an inert transgenic locus via cytoplasmic maternal inheritance. This results in a stable epigenetic conversion process, which can be performed recurrently--a phenomenon termed paramutation and discovered in Maize 60 y ago. Paramutation in Drosophila corresponds to the first stable paramutation in animals and provides a model system to investigate the epigenetically induced emergence of a piRNA-producing locus, a crucial step in epigenome shaping. In this Extra View, we discuss some additional functional aspects and the possible molecular mechanism of this piRNA-linked paramutation.
authors.affiliation: Epigenetic Repression and Mobile DNA; Laboratoire Biologie du Développement; UMR7622; CNRS-Université Pierre et Marie Curie; Paris, France.
authors.forename: Augustin
authors.initials: A
authors.lastname: de Vanssay
authors.affiliation: Drosophila Genetics and Epigenetics; CNRS URA2578; Institut Pasteur; Paris, France.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Bougé
authors.affiliation: Epigenetic Repression and Mobile DNA; Laboratoire Biologie du Développement; UMR7622; CNRS-Université Pierre et Marie Curie; Paris, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Boivin
authors.affiliation: Epigenetic Repression and Mobile DNA; Laboratoire Biologie du Développement; UMR7622; CNRS-Université Pierre et Marie Curie; Paris, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Hermant
authors.affiliation: Epigenetic Repression and Mobile DNA; Laboratoire Biologie du Développement; UMR7622; CNRS-Université Pierre et Marie Curie; Paris, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Teysset
authors.affiliation: Epigenetic Repression and Mobile DNA; Laboratoire Biologie du Développement; UMR7622; CNRS-Université Pierre et Marie Curie; Paris, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Delmarre
authors.affiliation: Drosophila Genetics and Epigenetics; CNRS URA2578; Institut Pasteur; Paris, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Antoniewski
authors.affiliation: Epigenetic Repression and Mobile DNA; Laboratoire Biologie du Développement; UMR7622; CNRS-Université Pierre et Marie Curie; Paris, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Ronsseray
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics*; D044127:Epigenesis, Genetic; D005260:Female; D005786:Gene Expression Regulation; D049750:Genome, Insect; D008297:Male; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D034741:RNA, Small Interfering
keywords: cellular memory; epigenetics; heterochromatin; piRNAs; transposable elements